This invention relates to a film forming method and apparatus for forming a metal-contained film such as a titanium film on a to-be-processed object such as a semiconductor wafer.
In general, to manufacture a semiconductor integrated circuit, a plurality of desired elements and/or wiring are formed on a substrate such as a semiconductor wafer by repeating processes which include film forming and pattern etching processes. Materials with a low electric resistance, of course, and also a high anti-corrosion must be used to form wiring for connecting the elements, a metallic contact for each element, or a metallic barrier for suppressing absorption of Si from the substrate. To this end, there is a tendency to use refractory metals such as Ti (titanium), W (tungsten), or Mo (molybdenum). Among these metals, Ti and TiN (titanium nitride) films are used in many cases since they show excellent electric and anti-corrosion characteristics.
Ti films are formed generally by plasma CVD (Chemical Vapor Deposition) using TiCl.sub.4 (titanium tetrachloride) and H.sub.2 gases as material gases. On the other hand, TiN films are formed by plasmaless CVD using TiCl.sub.4 and N.sub.2 gases as material gases, or by plasma CVD in the atmosphere of nitrogen gas.
A susceptor used in a film forming apparatus for performing the above-described film forming is generally made of ceramic such as AlN (aluminum nitride) which shows excellent heat resistance or anti-corrosion. The ceramic susceptor is rather expensive. Further, since ceramic itself has a low electric conductivity, it is possible that a potential difference will occur, during plasma CVD, in the object-mounting surface of the ceramic susceptor, and/or the susceptor itself and, for example, a peripheral wall portion of a process chamber, and hence that plasma of a stable state will not be generated in the process space to cause variations in plasma concentration in the space.
It is considered that occurrence of such a potential difference is suppressed by forming the susceptor of a metal with high conductivity, in order to stabilize plasma. In this case, however, so-called heavy metal contamination will occur in which semiconductor wafers mounted on the susceptor are contaminated by a metal such as iron, nickel, chromium, and manganese contained in the susceptor. Therefore, this method cannot be employed.
Further, it is considered that a ceramic coating layer is strongly attached to the surface of the metallic susceptor beforehand to prevent the heavy metal contamination. However, in this case, the coating layer may come off the susceptor or crack after the film forming is repeated, since the metallic susceptor and the ceramic coating layer have different coefficient of thermal expansion.
In addition, in the case of using ceramic, semiconductor wafers cannot be heated efficiently since ceramic has a low thermal conductivity.